The present invention relates to compositions based on monoaspartic acid esters and polyaspartic acid esters, a process for their production, and their use as reactive components for polyisocyanates in two-component polyurethane systems.
Two-component (2K) coating agents that contain as binder a polyisocyanate component in combination with a component reactive with respect to isocyanate groups, in particular a polyhydroxyl component, have been known for a long time. They are suitable for the production of high-quality coatings that are hard, elastic and resistant to abrasion and solvents, and that in particular can also be formulated to resist weathering.
In the field of 2K-polyurethane coating technology, specific ester group-containing secondary polyamines have recently become established that are in particular suitable, in combination with lacquer polyisocyanates, as binders in low-solvent or solvent-free high-solid coating compositions and that permit a rapid hardening of the coatings at low temperatures.
These secondary polyamines are the so-called polyaspartic acid esters such as are described for example in EP-A 0 403 921. Their use alone or mixed with further components reactive with respect to isocyanate groups in 2K-PUR coating agents is described for example in EP-A 0 403 921, EP-A 0 639 628, EP-A 0 667 362, EP-A 0 689 881, U.S. Pat. No. 5,214,086, EP-A 0 699 696, EP-A 0 596 360, EP-A 0 893 458, DE-A 19 701 835 and U.S. Pat. No. 5,243,012.
The synthesis of polyaspartic acid esters is carried out by the addition of primary amines to an activated carbon double bond of vinylogous carbonyl compounds, as contained for example in maleic or fumaric acid esters and which is described in detail in the relevant literature (Houben Weyl, Meth. d. Org. Chemie Vol. 11/1, 272 (1957); Usp. Khim. 1969, 38,1933).
It has been found that this reaction sometimes does not go to completion during the synthesis (for example after 24 hours while stirring at 60xc2x0 C.). The conversion rate of the reaction depends decisively on the type of primary polyamines used. The degree of conversion (measured on the basis of the concentrations of free, unreacted maleic and fumaric acid esters) after 1 day with 1,5-diamino-2-methylpentane is 90 to 93%. In contrast to this the degree of conversion when using a cycloaliphatic polyamine with sterically hindered amino groups (for example 4,4xe2x80x2-diamino-3,3xe2x80x2-dimethyldicyclohexylmethane) is only 77%. A complete or almost complete conversion is sometimes achieved only after several months.
These incompletely reacted products contain unreacted primary amino groups and possibly also free primary polyamines as well as the corresponding amount of unreacted maleic or fumaric acid esters. As a result, after the production of the products the latter continue to react during subsequent storage and accordingly the viscosity of the reaction mixture rises constantly until complete conversion has been attained. In addition, the reactivity of the product with respect to isocyanates decreases with the reduction in the concentration of primary amino groups. It is therefore sometimes not possible to ensure the establishment of a reproducible pot life.
Various solutions to the problem have already been described in the prior art, which however still do not provide ultimately satisfactory results.
It is possible to extend the reaction time or increase the reaction temperature. The first solution is often excluded for economic reasons. Increasing the reaction temperature to for example 80xc2x0 C. or even 100xc2x0 C. leads in turn to a increase in the color number of the product.
EP-A 0 667 362 and U.S. Pat. No. 5,243,012 describe extending the pot life of 2K-PUR binders based on polyisocyanates and polyaspartic acid esters by adding zeolites and/or organotin(IV) compounds. These measures are however only ameliorative and sometimes adversely affect other properties, and may for example lead to a turbidity of the lacquer or accelerate the NCO/OH reaction in the binder.
U.S. Pat. No. 5,821,326 describes how the reaction to produce monoaspartic acid and polyaspartic acid esters can be catalyzed by five-membered aromatic ring compounds. Although the catalysts used do indeed permit a more rapid conversion of the components, nevertheless in none of the quoted examples had a complete conversion of the reaction mixture been achieved within a reaction time of four days at 60xc2x0 C. During the subsequent storage of the product mixture the viscosity of the product rises on account of the incomplete reaction.
In U.S. Pat. No. 5,216,170 the excess fumaric acid ester is removed by means of distillation and thus withdrawn from the reaction. This process is however time-consuming and energy-intensive and therefore does not provide a basis for a technically feasible process.
Accordingly, it is an object of the present invention to provide monoaspartic acid ester and polyaspartic acid ester systems that have an improved viscosity stability and thus storage stability without the quality of the resulting binders and/or coatings being adversely affected.
This object may be achieved by a thiol compound to an incompletely reacted reaction mixture, which during storage leads to a significantly lower rise in viscosity of the product and moreover the end product does not suffer from malodorous side effects due to the thiol compounds that are used. The effect of adding the thiol compound is that the unreacted portion of the vinylogous carbonyl compound is no longer available to undergo further reaction with the primary amines.
The present invention relates to a composition containing monoaspartic acid esters and polyaspartic acid esters of formula (I),
Xxe2x80x94[NHxe2x80x94CH(CH2xe2x80x94COOR2)xe2x80x94COOR1]mxe2x80x83xe2x80x83(I) 
in which
X represents an m-valent organic radical obtained by removing the primary amino group or groups from a corresponding monoamine or polyamine in the molecular weight range from 60 to 6000 containing (cyclo)aliphatically or araliphatically bound primary amino groups,
R1 and R2 represent identical or different organic radicals, and
m represents an integer xe2x89xa71,
as well as an addition product prepared from a compound of formula (II) (component A),
R1OOCxe2x80x94CHxe2x95x90CHxe2x80x94COOR2xe2x80x83xe2x80x83(II) 
wherein the radicals R1 and R2 have the aforementioned meanings,
and a thiol compound of the formula (III) (component B),
[HS]nxe2x80x94R3xe2x80x83xe2x80x83(III) 
in which
R3 represents an n-valent organic radical optionally containing one or more heteroatoms, which may also contain other functional groups that are reactive or inert with respect to isocyanates, and
n represents an integer xe2x89xa71 and xe2x89xa64.
The compositions according to the invention are products having improved viscosity stability.
The present invention also relates to a composition containing monoaspartic acid esters and polyaspartic acid esters of formula (I),
Xxe2x80x94[NHxe2x80x94CH(CH2xe2x80x94COOR2)xe2x80x94COOR1]mxe2x80x83xe2x80x83(I) 
in which
X represents an m-valent organic radical containing one or more heteroatoms, obtained by removing the primary amino group or groups from a corresponding monoamine or polyamine in the molecular weight range from 60 to 6000 containing (cyclo)aliphatically or araliphatically bound primary amino groups, which may contain further functional groups that are reactive with respect to isocyanate groups and/or are inert at temperatures up to
R1 and R2 represent identical or different alkyl radicals each having 1 to 18 carbon atoms and more particularly preferably represent identical or different alkyl radicals each having 1 to 8 carbon atoms, and
m represents an integer xe2x89xa72 and more preferably =2,
as well as an addition product prepared from a compound of formula (II) (component A),
R1OOCxe2x80x94CHxe2x95x90CHxe2x80x94COOR2xe2x80x83xe2x80x83(II) 
wherein the radical R1 and R2 have the aforementioned meanings,
and a thiol compound of the formula (III) (component B),
[HS]nxe2x80x94R3xe2x80x83xe2x80x83(III) 
in which
R3 represents an n-valent organic radical optionally containing one or more heteroatoms, which may also contain other functional groups that are reactive or inert with respect to isocyanates, and
n represents an integer xe2x89xa71 and xe2x89xa64.
The present invention also provides a process for the production of monoaspartic acid esters and polyaspartic acid esters of formula (I)
Xxe2x80x94[NHxe2x80x94CH(CH2xe2x80x94COOR2)xe2x80x94COOR1]mxe2x80x83xe2x80x83(I) 
by reacting monoamines or polyamines of formula (IV) (component C),
X[xe2x80x94NH2]mxe2x80x83xe2x80x83(IV) 
with compounds of formula (II) (component A)
R1OOCxe2x80x94CHxe2x95x90CHxe2x80x94COOR2xe2x80x83xe2x80x83(II) 
with a residual content of double bonds of 2 to 15% measured in terms of the double bonds present at the start of the reaction
in the presence of at least one thiol compound of the formula (III) (component B),
[HS]nxe2x80x94R3xe2x80x83xe2x80x83(III), 
in which
R3represents an n-valent organic radical optionally containing one or more heteroatoms, which may also contain other functional groups that are reactive or inert with respect to isocyanates, and
n represents an integer xe2x89xa71 and xe2x89xa64.
The process according to the invention for the production of monoaspartic acid esters and/or polyaspartic acid esters of formula (I) is preferably carried out in two stages. In the first stage the components A and C are reacted at temperatures between 0xc2x0 C. and 100xc2x0 C., preferably 20xc2x0 C. to 80xc2x0 C. and more preferably 20xc2x0 C. to 60xc2x0 C., in a ratio of equivalents of primary amino groups of the component C to the Cxe2x95x90C double bond equivalents of the component A of 1:1.2 to 1.2:1, preferably however 1:1.05 to 1.05:1, until the residual content of double bonds measured in terms of the double bonds present at the start of the reaction is 2 to 15%, preferably 5 to 10%. In the second stage unreacted double bond equivalents of the component A are reacted in the temperature range from 0xc2x0 C. to 100xc2x0 C., preferably 20xc2x0 C. to 80  C. and more preferably 20xc2x0 C. to 60xc2x0 C., with the thiol groups of the component B in a molar ratio of 1.5:1 to 1:1, preferably 1.2:1 to 1:1, and more preferably 1.05:1.
A further suitable embodiment of the process according to the invention is the production of the monoaspartic acid and/or polyaspartic acid esters in three stages, wherein two different amines of the formula (IV) are used as component C1 and C2. In the first stage the components A and C1 are reacted at temperatures between 0xc2x0 C. and 100xc2x0 C., preferably 20xc2x0 C. to 80xc2x0 C. and particularly preferably 20xc2x0 C. to 60xc2x0 C., in a ratio of the equivalent of the primary amino groups of the component C1 to the Cxe2x95x90C-double bond equivalents of the component A of 1:1.3 to 1:2, but preferably 1:1.5 to 1:1.7, until the residual content of primary amino groups is 0 to 15%, preferably 0 to 10%. The mixture is then reacted in the second stage with the component C2 in a temperature range from 0  C. to 100  C., preferably 20xc2x0 C. to 80  C. and particularly preferably 20xc2x0 C. to 60xc2x0 C., so that the ratio of the sum of the equivalents of the amino groups of components C1 and C2 to the double bond equivalents of the component A is 1:1.2 to 1.2:1, preferably however 1:1.05 to 1.05:1. The reaction is carried out until 2 to 15%, preferably 5 to 10% of the double bonds still remain. In the third stage unreacted double bond equivalents of the component A are reacted with the thiol groups of the component B in a molar ratio of 1.5:1 to 1:1, preferably 1.2:1 to 1:1 and particularly preferably 1.05:1, in a temperature range from 0  C. to 10xc2x0 C., preferably 20  C. to 80xc2x0 C. and particularly preferably 20xc2x0 C. to 60xc2x0 C.
In the process according to the invention, in principle all known monoamines and polyamines having at least one primary amino group and that correspond to the formula (IV) may be used as component C.
Particularly suitable primary monoamines according to formula (IV) (m=1) include those monoamines that contain in their organic radical X one or more further functional groups that are either reactive or inert with respect to isocyanate groups. Examples include aminofunctional silanes such as for example 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane or also aminoalcohols such as for example ethanolamine, propanolamine or isopropanolamine.
Preferred components C include polyamines of the formula (IV) where m represents an integer greater than or equal to 2. Examples include ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, 2,5-diamino-2,5-dimethylhexane, 1,5-diamino-2-methylpentane (Dytek A, DuPont), 1,6-diaminohexane, 2,2,4- and/or 2,4,4-trimethyl-1,6-diaminohexane, 1,11-diaminoundecane, 1,12-diaminododecane or triaminononane.
Also suitable are higher molecular polyether polyamines with aliphatically bound primary amino groups such as are marketed by the company Huntsman, for example under the trade name Jeffamin. Polyamines of the formula (IV) in which m=2 and X represents a cyclic hydrocarbon radical with at least one cyclic carbon ring are more preferred in the process according to the invention. Examples of diamines that may particularly preferably be used include 1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane (IPDA), 2,4- and/or 2,6-hexahydrotoluylenediamine (H6TDA), isopropyl-2,4-diaminocyclohexane and/or isopropyl-2,6-diaminocyclohexane, 1,3-bis-(aminomethyl)cyclohexane, 2,4xe2x80x2- and/or 4,4xe2x80x2-diaminodicyclohexylmethane, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodicylcohexylmethane (Laromin C 260, BASF AG), the isomeric diaminodicylcohexylmethanes containing a methyl group as core substituent (xe2x95x90C-mono-methyidiaminodicyclohexylmethanes), 3(4)-aminomethyl-1-methylcyclohexylamine (AMCA) as well as araliphatic diamines, for example 1,3-bis-(aminomethyl)benzene.
Suitable components A include maleic or fumaric esters of formula (II) wherein R1 and R2 represent identical or different organic radicals each having 1 to 18 carbon atoms. Preferably R1 and R2 independently of one another represent linear or branched alkyl radicals with 1 to 8 carbon atoms.
Examples of component A include maleic acid dimethyl ester, diethyl ester, di-n-propyl or isopropyl ester, di-n-butyl ester, di-2-ethylhexyl ester or the corresponding fumaric acid esters.
Suitable components B include mercapto compounds of the general structural formula (III). Preferred mercapto compounds include trimethylolpropane-tri-(mercaptopropionate), pentaeryth ritol-tetra-(3-mercaptopropionate), glycol-di-(3-mercaptopropionate), glycol-dimercaptoacetate, trimethylolpropane-trithioglycolate, 2-ethylhexylthioglycolate, n-propylthio-glycolate and/or isopropylthioglycolate, n-, iso- and/or tert.-butylthio-glycolate, mercapto diethyl ether, cyclohexylmercaptan, ethanedithiol, 1,4-butane-dithiol, 1,6-hexanedithiol, dodecanedithiol, didodecanedithiol, dimercaptobenzothiazole, allylmercaptan, benzylmercaptan, 2-mercaptoethanol, 2,3-dimercapto-propanol, xcex1,xcex1xe2x80x2-dimercapto-p-xylene, thiosalicylic acid, thiolactic acid, mercaptopropionic acid, mercaptoacetic acid, mercaptopyridine, dithioerythritol, 6-ethoxy-2-mercaptobenzothiazole, d-limonene-dimercaptan as well as liquid polysulfides such as are marketed by Marton Int. GmbH under the trade name LP, or mixtures thereof.
Particularly suitable examples of component B include esters of thioglycolic acid with linear or branched alcohols having at least 4 carbon atoms. Also suitable are thiols that contain further groups reactive with respect to isocyanates. Examples that may be mentioned here include 2,3-dimercapto-1-propanol, 2-mercaptoethanol, 3-mercapto-1,2-propanediol, ethylene glycol monothioglycolate, 2-hydroxyethyl-3-mercaptopropionate, 6-mercapto-1-hexanol, glycerol monothioglycolate, 4-mercaptobutanol, 11-mercapto-1-undecanol, cysteinol and glyceryl-3-mercapto-propionate. Also suitable are aliphatic monofunctional thiols having molecular weights of more than 146 g/mole, such as for example 1-octanethiol, dodecanethiol and didodecanethiol. Less preferred are mixtures of the aforementioned thiol compounds.
The production of the monoaspartic acid esters or polyaspartic acid esters of formula (I) according to the invention may be carried out in solution as well as in a solvent-free manner. The addition of solvents may however also take place only after the completion of the synthesis process, for example in order to reduce the viscosity. In principle all organic solvents are suitable as solvents, though of course it is preferred to use those solvents employed in coating technology. Examples include, though the list is not meant to be exhaustive, acetone, methyl ethyl ketone, methyl isobutyl ketone, n-butyl acetate, methoxypropyl acetate, toluene, xylene as well as higher aromatic solvents such as are marketed by Exxon-Chemie under the trade name Solvesso.
In a preferred embodiment of the invention the composition according to the invention contains
a) 98 to 55 wt. % of a monoaspartic and polyaspartic acid ester of formula (I),
b) 45 to 1 wt. % of an addition product prepared from a component A of formula (II) and a component B of the formula (III),
c) 0 to 3 wt. % of free component A of formula (II),
d) 0 to 1 wt. % of free component C of the formula (IV),
with the proviso that the sum of a) to d) totals 100 wt. % based on a) to d),
as well as optionally free component B of the formula (III) and optionally the conventional additives.
In a particularly preferred embodiment the composition according to the invention contains
a) 97 to 71 wt. % of a monoaspartic and polyaspartic acid ester of formula (I),
b) 29 to 3 wt. % of an addition product prepared from a component A of formula (II) and a component B of the formula (III),
c) 0 to 0.5 wt. % of free component A of formula (II),
d) 0 to 0.5 wt. % of free component C of the formula (IV),
with the proviso that the sum of a) to d) totals 100 wt. % based on a) to d),
as well as optionally free component B of the formula (III) and optionally the conventional additives.
The compositions according to the invention can be used directly after the completion of the synthesis process and, as regards reactivity, are stable over a period of several months and exhibit a significantly improved viscosity stability. On account of their low internal viscosity compared to the monoaspartic and polyaspartic acid esters that have been produced according to processes known in the prior art, the compositions according to the invention represent valuable reaction partners for polyisocyanates in low-solvent or solvent-free two-component polyurethane lacquers and coatings.
The present invention also provides for the use of the compositions according to the invention as reactive component in two-component polyurethane systems or for the production of prepolymers.
The two-component (2K) polyurethane systems containing the compositions according to the invention may then be used as coating agents for the production of coatings.
The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.